In a conventional display device, high conductivity materials such as copper, aluminum and the like have gradually replaced the traditional materials and become the preferred body material for the metal electrodes. A major technology facilitating the above change is the use of protection layer, i.e., by forming protection layers on both sides of the copper layer or aluminum layer using materials with more stable materials such as molybdenum, niobium or the like, it is possible to prevent atom diffusion, prevent oxidation of materials, improve surface properties and improve contact resistance. However, the above change may cause new problems in the conventional manufacturing process. During the processes of etching via holes and connecting electrodes, the etching is generally performed to a depth exceeding the depth of the via hole with reference to the deepest via hole, to prevent any partial under-etching of the via hole. While particularly in the scheme of using the copper electrode or aluminum electrode, the above over etching process may cause etching damage to the protection layer. If the protection layer at the bottom of the via hole is penetrated by the etching, the copper or aluminum without protection may undergo diffusion or oxidation, resulting in a very large contact resistance or even an open circuit at the via hole. Currently, in order to protect the protection layer from been penetrated by over etching, the thickness of the upper protection layer is significantly increased, which results in not only increasing the consumption of the target material and the time for forming the film, but also increasing the overall thickness of the substrate and steps in the structure, thereby causing various problems regarding cost, the productivity and element performance.
It should be noted that, information disclosed in the above background portion is provided only for better understanding of the background of the present disclosure, and thus it may contain information that does not constitute the prior art known by those ordinary skilled in the art.